1. Field of the Invention
The present invention relates generally to a battery protection circuit module device and, more particularly, to a battery protection circuit module device, which is capable of significantly preventing a reduction in the duration of use of a battery attributable to a voltage drop resulting from peak current and on-resistance occurring upon discharging because the plurality of switching devices of a battery protection circuit module is configured to be selectively used upon charging or discharging and thus the on-resistance of the switching devices occurring upon discharging is reduced to half, which is capable of considerably reducing the manufacturing cost required to manufacture a charger integrated circuit (IC) because a low rated device can be used in the charger IC, and which is capable of increasing the stability and reliability of a portable product because a charger and a system other than a protection circuit module can remain insulated from a stationary device even when the portable product is coupled to the stationary device and thus the portable product is not influenced by abnormal input from the stationary device.
2. Description of the Related Art
Currently, in many mobile and portable products, a large amount of power is required to drive a high-performance processor IC so as to perform various functions and multi-processing, and to drive a large-screen display. The capacities of batteries tend to increase in order to meet consumers' desire for long-term battery use from a single charge.
Efforts to increase the system efficiency so as to make batteries usable for a long time as well as to increase the capacities of the batteries have been made. In particular, due to the application of a high-performance processor, the amount of peak current that is instantaneously discharged is very large, and thus voltage drop attributable to the resistance of a power line extending from the battery to the system is very high. This high voltage drop causes the system to consider the current state of the battery to be lower than the actual charge level, so that system shutdown attributable to low battery voltage occurs at an early stage, thereby reducing the duration of use of the battery. Since such voltage drop also influences efficiency, a protection circuit module, including switches with low on-resistance, is required to reduce the voltage drop.
The protection circuit module is a protection circuit that is provided for a battery in order to enable the battery, such as a lithium-ion battery or a lithium polymer battery, to be stably operated. It is essentially applied to the battery packs of almost all mobile and portable devices.
A protection circuit module is a module that is essentially applied to batteries, such as lithium-ion batteries and lithium polymer batteries, in order to control the charging and discharging of the batteries and protect the batteries from abnormal states such as high/low voltage, excessive current and high temperature. The protection circuit module includes two switches and a control circuit configured to operate these switches.
In the conventional protection circuit module, two switches are turned on regardless of whether the battery is charged with power or power has been discharged from the battery, and the two switches are connected in series. Therefore, the sum of the on-resistances of respective switches becomes the on-resistance of protection circuit module switches.
That is, in terms of a structure, on-resistance that doubles the on-resistance of a single switch is generated. The reason why the two switches are connected in series is that electrical switches fabricated in the form of semiconductors generally have an electrical connection path formed in a parasitic manner. In the case of a widely used N-channel MOSFET, a parasitic diode is formed from its source to its drain, so that an electrical connection path is presented by the diode in the direction from the source to the drain even when the N-channel MOSFET is turned off. Insulation is required to electrically separate the battery from the charger or system. If a single N-channel MOSFET is used, electrical insulation cannot be achieved in one direction. In contrast, if two N-channel MOSFETs are used and form a common drain structure, the cathodes of parasitic diodes are opposite each other, so that an insulation state in which an electrical connection path has been completely blocked in the opposite directions can be maintained.
FIGS. 1 and 2 show conventional battery protection circuit module devices.
FIG. 1 is an application circuit diagram of a portable system to which one conventional battery protection circuit module device has been applied, and FIG. 2 is the other conventional battery protection circuit module device.
Referring to FIG. 1, the conventional battery protection circuit module device includes:
a charging unit 1 configured to include first and second MOSFET switches M1 and M2, and to supply externally input power to a battery BAT or a system 3;
a battery protection circuit module 2 configured to include the battery BAT, third and fourth MOSFET switches M5 and M6 connected in series to the minus terminal of the battery BAT, and configured to be selectively turned on and off under the control of a PCM controller 21 so that the battery BAT is selectively and electrically connected to and disconnected from the outside; a resistor R1 and a capacitor C1 configured to detect the voltage of the battery BAT and to supply the voltage of the battery BAT to the PCM controller 21 as driving power; and the PCM controller 21 configured to control the third and fourth MOSFET switches M5 and M6 based on the state of the voltage of the battery BAT so that the third and fourth MOSFET switches M5 and M6 are selectively turned on and off and thus the battery BAT is selectively charged and discharged; and
the system 3 configured to be operated using the voltage of the battery BAT or externally input voltage.
The third and fourth MOSFET switches M5 and M6 are connected via a common drain structure so that their drains are opposite each other. Parasitic diodes formed in the MOSFET switches M5 and M6 in a parasitic manner are connected so that their cathodes are opposite each other. Accordingly, when the first and second MOSFET switches M5 and M6 are turned off, electrical insulation can be achieved.
The PCM controller 21 implements the basic functionality of performing charging when a power voltage source is connected between a VBAT terminal and a GND terminal and performing discharging when a load is connected therebetween, and additionally detects an abnormal state and controls the third and fourth MOSFET switches M5 and M6 in order to protect the battery BAT from excessive charging, excessive discharging, excessive current, high temperature or a short circuit.
The operation of the conventional battery protection circuit module device will now be described.
Upon the charging or discharging of the battery BAT, the third and fourth MOSFET switches M5 and M6 are turned on under the control of the PCM controller 21, and the battery BAT is charged with external power input through the charging unit 1, and power stored in the battery BAT is discharged and supplied to the system 3.
Meanwhile, FIG. 2 shows the other conventional battery protection circuit module device.
The battery protection circuit module 2 of the other conventional battery protection circuit module device includes:
a battery BAT, first and second switches S5 and S6 connected in series to the plus terminal of the battery BAT, and configured to be selectively turned on and off under the control of a PCM controller 21 so that the battery BAT is selectively and electrically connected to and disconnected from the outside; a resistor R1 and a capacitor C1 configured to detect the voltage of the battery BAT and to supply the voltage of the battery BAT to the PCM controller 21 as driving power; and the PCM controller 21 configured to control the first and second switches S5 and S6 based on the state of the voltage of the battery BAT so that the first and second switches S5 and S6 are selectively turned on and off and thus the battery BAT is selectively charged and discharged
The other conventional battery protection circuit module device is configured such that the first and second switches S5 and S6 are connected to the plus (+) terminal of the battery BAT. More stable operation can be achieved against abnormal charging and discharging because the first and second switches S5 and S6 are connected to the plus terminal of the battery BAT, and more accurate control can be achieved because the PCM controller 21 comes to have a stable reference electric potential (ground).
However, the conventional technology is configured such that the two MOSFET switches or the two switches are turned on upon discharging, so that a voltage drop attributable to a peak current occurs due to double on-resistance when power is discharged from the battery to the system, thereby reducing the duration of use of the battery. Accordingly, there is a demand for a scheme for reducing on-resistance.
Up to the present day, a scheme for reducing the on-resistance of each switch has been pursued. Larger switches are required to reduce on-resistance, and thus the cost increases. Furthermore, the increase in the areas of the switches is limited by the mechanical problem of the battery structure (mobile and portable products tending to have slim shapes), and thus there is a demand for a new scheme.
Currently, a protection circuit module structure and a charger and system for charging a battery use the same ground. That is, an input power voltage source (normally, an adapter) configured to supply power in order to perform charging using external power, a charger, and a portable system share a common ground. Since a portable product is normally insulated from a stationary device and is supplied with power by an internal power source, that is, a battery, the internal voltage of the portable product cannot be increased above battery voltage unless a special boosting circuit is provided. However, since it is necessary to connect to the stationary device so as to perform charging and data signal transfer and exchange, design is carried out on a high rated voltage basis in order to deal with the stationary device. For this reason, the battery voltages of mobile devices are mostly 4.2 V in the case where a single cell is used, whereas the input voltages of chargers configured to charge a battery are normally a rated voltage of 28 V. This is intended to deal with the abnormal operation of the power voltage source and an abnormal external input such as electrostatic discharge (ESD) or surge.
Accordingly, devices with high rated voltage should be used in the charger circuit, and therefore the manufacturing cost of the charger increases. The charger contains a common drain structure, in which two switches are opposite each other and connected in series like the control switches of the protection circuit module, in order to block reverse current flowing in the direction from the battery to a power voltage source in the case of no charging, that is, in order to insulate the battery from an input terminal power voltage source, like the PCM circuit used for the battery, and is intended to reduce the on-resistance of the switches in order to improve charging efficiency. However, the areas of the switches should be increased so as to achieve high rated voltage and low on-resistance, and therein the problem of incurring the increase in the manufacturing cost arises.